"Butchers, prostitutes, those guilty of the five most heinous crimes, outcasts, the underprivileged: all are utterly the substance of existence and nothing other than total bliss."The Supreme Source - The Kunjed Gyalpo
The Fundamental Tantra of Dzogchen Semde

Tibetanised Sanskrit pronunciation can vary greatly because of the variety of Tibetan dialects.

"My religion is not deceiving myself."Jetsun Milarepa 1052-1135 CE

"Butchers, prostitutes, those guilty of the five most heinous crimes, outcasts, the underprivileged: all are utterly the substance of existence and nothing other than total bliss."The Supreme Source - The Kunjed Gyalpo
The Fundamental Tantra of Dzogchen Semde

Personally I learned goo-roo-byah, but I've also seen texts where it's written as gurubhye (i.e. goo-roo-byey). I think it has to do with the proper vocative case in Sanskrit.

When I do prostration I use gurubhya out of habit. I'll use gurubhye when I see it in av text.

The vast majority of my lamas are Khampas, and from the Nangchen as Derge areas specifically. Not sure how that affects. Pronunciation in Tibetanized Sanskrit, as noted by Greh

"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, a common corpse is found in the bed of a great scholar." ~ Karma Chagme

Three syllables. The ə is a mid-central vowel, or a schwa. Click the ə here.

The "J" is pronounced like the y in "grab your umbrella".

The B is aspirated. Chances are if you are a native English speaker you might already aspirate most of your B's depending on your accent.

Don't round your O (i.e. pronouncing it with a little 'w' at the end, an English habit, if you have it).

Obviously this is a "proscriptive" pronunciation. Sanskrit pronunciation is like Latin pronunciation. Anything goes.

The French pronounce Latin in the French manner, the Polish in the Polish manner, etc.

歸命本覺心法身常住妙法心蓮臺本來莊嚴三身徳三十七尊住心
城遠離因果法然具普門塵數諸三昧無邊徳海本圓滿還我頂禮心諸佛In reverence for the root gnosis of the heart, the dharmakāya,
for the ever present good law of the heart, the lotus terrace,
for the inborn adornment of the trikāya, the thirty-seven sages dwelling in the heart,
for the that which is removed from seed and fruit, the upright key to the universal gate,
for all boundless concentrations, the sea of virtue, the root perfection,
I prostrate, bowing to the hearts of all Buddhas.胎藏金剛菩提心義略問答鈔, Treatise on the teaching of the gnostic heart of the womb and the diamond, T2397.1.470c5-8